Alvin Paral-Liner Parallel Rules feature rigid phenolic construction with a black satin finish. These mobile straightedges afford frictionless operation via the floating action of the nylon rollers mounted on the underside of the blade. The rollers are retractable at a touch, stopping the blade for precise drawing. The edges are made of elevated Plexiglas, preventing ink smears. Steel ball-bearing pulleys provide smooth movement of the straightedge. Includes all mounting hardware and installation instructions.